1. Field of the Invention
The invention relates to ceramic matrix composites including BN coated fibers and matrices.
2. Description of the Related Art
Ceramics has been used as heat-resistive material, but has shortcomings such as high brittleness caused by inherent characteristics thereof and low reliability with respect to strength. Hence, there has been developed fiber-reinforced ceramics toughened by incorporating fibers into ceramics matrices. In particular, there has been developed ceramic matrix composites manufactured by coating fibers with carbon (C) or boronanitoride (BN), and then bonding the fibers to ceramics. For instance, U.S. Pat. Nos. 4,869,943 and 4,885,199 have suggested ceramic matrix composites having BN interface by coating fibers with BN.
An upper limit in ambient temperature at which ceramic matrix composites having BN interface can be used is about 1000 degrees centigrade. Beyond 1000 degrees centigrade, BN is remarkably oxidized. As oxidized B.sub.2 O.sub.3 has a melting point of about 500 degrees centigrade, bonding force between fibers and matrixes is weakened at 1000 degrees centigrade or greater in air, resulting in that it is impossible for the ceramic matrix composites to keep a certain strength thereof. However, there has been long desired ceramic matrix composites which can be used at 1000 degrees centigrade or greater, preferably up to about 1400 degrees centigrade.